Complement receptor type 1 (CR1) on erythrocytes shows an inherited numerical polymorphism which correlates with a HindIII-RFLP (restriction fragment length polymorphism) of the CR1 gene in various populations. To investigate the relationship between CR1 density polymorphism and disease severity, we typed 185 Thai patients with acute falciparum malaria (55 severe and 130 uncomplicated) for their genotypes of this polymorphism. The level of expression of erythrocyte CR1 from 42 randomly selected patients was measured by enzyme-linked immunosorbent assay (ELISA). We observed a significantly higher frequency of homozygotes of the CR1 low density allele (LL) among the severe group as compared to the uncomplicated group (P = 0.005). CR1 expression on erythrocytes from patients with the LL genotype was significantly lower than homozygotes with the high density allele (HH) (P < 0.0001) and heterozygotes (HL) (P = 0.013). The results suggest that a genetically-determined low CR1 density on erythrocytes may be a risk factor for developing a more severe form of malaria in Thai subjects.

The influence of alpha(+)-thalassemia on malaria in pregnancy was assessed in a cross-sectional study of 530 women in Ghana. Plasmodial infections, alpha(+)-thalassemia, serum levels of C-reactive protein, and antimalarial drugs in urine were determined. The alpha-globin genotypes did not correlate with the prevalence of Plasmodium falciparum-infection and parasite densities. However, Plasmodium malariae tended to be more frequent in alpha(+)-thalassemic women (P = 0.05). Excluding women with residual antimalarials, a significant excess of P. malariae was observed in alpha(+)-thalassemic individuals. Febrile responses (P = 0.05) and inflammation (CRP > 0.6 mg/dl, P = 0.06) appeared to be less common in infected alpha(+)-thalassemic women and were also comparatively rare in parasitemic individuals who harbored double species infections with P. falciparum and P. malariae. Plasmodium malariae may influence the pathogenesis of falciparum malaria leading to a low prevalence of inflammation and febrile responses in alpha(+)-thalassemic women.

In areas highly endemic for malaria, individuals are frequently found to be infected simultaneously with multiple Plasmodium falciparum clones. This raises the question of whether all parasite clones produce gametocytes equally or whether gametocytogenesis is suppressed in some clones. In order to assess this in epidemiological studies, polymorphic genes specifically expressed in gametocytes could be analyzed by both amplification of genomic DNA from blood samples and by reverse transcribed polymerase chain reaction amplifying expressed gametocyte-specific genes only. Here we report the analysis of diversity in the three gametocyte-specific genes Pfs16, Pfs48/45, and Pfs230. In addition to the previously published data, limited polymorphism was found in the coding sequences of Pfs16 and Pfs48/45. Larger polymorphism was identified in Pfs230, which might allow the development of a discriminating PCR-based genotyping scheme for transmission studies. However, the limited polymorphism in Pfs16 and Pfs48/45 renders these molecules poorly useful for such studies.

St. Louis encephalitis (SLE) is endemic in Harris County, Texas. The disease is a public health concern in Houston, the largest city in Harris County, and in the state. Consequently, intensive surveillance for SLE virus in local mosquito populations is carried out by the Harris County Mosquito Control Division each year. In this study, we examined genetic variation among SLE isolates obtained during routine virus surveillance over a 13-year time period (1986-1999). St. Louis encephalitis virus isolates were tested for genetic variation using reverse transcription-polymerase chain reaction followed by single-strand conformation polymorphism (SSCP). The results indicated that multiple genotypes of the virus circulate in Harris County. During several years, the genotypes were restricted in their location, i.e., each general area within the county had a specific genotype of the virus. In other years, the various genotypes were widely distributed throughout the county. The presence of multiple distinct genotypes suggests that viruses with different biological characteristics may be circulating in Harris County, and that discrete foci of SLE virus activity occur simultaneously.

This study was conducted to evaluate the performance of two rapid non-microscopic assays: Plasmodium lactate dehydrogenase (pLDH) assay (OptiMAL) and Plasmodium falciparum histidine-rich protein 2 (PfHRP-2) assay (ICT Malaria). The assays were used to detect malaria infection in 515 immigrants living in Kuwait. The performance of both assays was compared to that of microscopy of Giemsa-stained thick blood films and to each other. Of the 515 patients tested, 163 were positive for malaria parasites by microscopy of thick blood film. Of these, 87 were infected with Plasmodium vivax parasites, 63 with P. falciparum, 1 with Plasmodium malariae, and 12 had mixed infections of P. falciparum and P. vivax. The PfHRP-2 assay detected 53 P. falciparum infections and, as expected, failed to detect all but one case of P. vivax. Three cases of mixed infections were also not detected by this assay. The pLDH assay detected 56 P. falciparum cases and 77 P. vivax infections but failed to detect 4 cases of mixed infections. Compared to microscopy, the performance of both the assays to diagnose P. falciparum infection was comparable. The sensitivity for the PfHRP-2 assay was 82% with a specificity of 99.0% and for the pLDH assay the sensitivity was 89% with a specificity of 99.5%. The PfHRP-2 assay detected 4 false positive cases, 2 of which were also detected by the pLDH assay. These patients reported treatment with chloroquine in the last 2-5 weeks. Though the immunocapture diagnostic assays may be helpful in certain situations, microscopy of thick blood film is still the method of choice in diagnosing imported malaria.

This is a report of a randomized, open, labeled study of the maintenance treatment of melioidosis using a combination of ciprofloxacin and azithromycin (Regimen A) for 12 weeks versus a combination of cotrimoxazole and doxycycline (Regimen B) for 20 weeks. The study was conducted at two tertiary-care hospitals in northeast Thailand. A total 65 patients were enrolled, 36 and 29, respectively, between August 1997 and July 1998. Subjects were randomly allocated to each arm of the trial, resulting in 32 treated under Regimen A and 33 in B. The main outcome was a culture-proven relapse in melioidosis. There were more relapses under Regimen A at 22% (7 of 32) than in Regimen B, 3% (1 of 33). The 19% difference in the rates was significant (95% confidence interval [CI]: 3% to 34%; exact P-value = 0.027). Based on our data, a combination of cotrimoxazole and doxycycline treatment for 20 weeks should be given further consideration as the maintenance therapy of choice for melioidosis.

Dihydropteroate synthase (dhps) and dihydrofolate reductase (dhfr) alleles were typed in 67 Malaysian Plasmodium falciparum isolates. The isolates were collected from two geographically distinct locations: 51 from Sabah, Malaysian Borneo, where sulfadoxine/pyrimethamine (SDX/PYR) is used to treat uncomplicated malaria and 16 from Peninsular Malaysia where in vivo resistance to SDX/PYR has been reported. A total of seven dhps alleles were identified with no significant difference in allele frequency between the 2 populations. Two of the dhps alleles described here have not been previously reported. Four dhfr alleles were detected in 67 P. falciparum isolates. Eighty-seven percent of the isolates from the Peninsula, where clinical SDX/PYR failure has been reported, had dhfr alleles with triple point mutations while all of the isolates from Sabah had dhfr alleles with 2 or less point mutations. The difference in dhfr allele frequency between the two populations was highly significant. There was no correlation between in vitro PYR response and accumulation of dhfr point mutations.

Two standard methods are available to infect mosquitoes with malaria parasites: direct feeding through the skin of the gametocyte carrier, and membrane feeding. Anopheles arabiensis collected at larval stages and reared in an insectary were fed in parallel by feeding on Plasmodium falciparum gametocyte carriers and by membrane feeding on venous blood of the same gametocyte carriers. Infection of mosquitoes was assessed at Day 7 post bloodmeal by oocyst count of the mosquito midguts. The following parameters were not significantly different between the two methods: the percentage of gametocyte carriers infective for at least one mosquito (52.4% through the skin versus 57.1% through the membrane), the mean infection rate of mosquitoes (10.0% versus 11.3%), the geometric mean oocyst number per mosquito (2.51 versus 3.83). In conclusion, infection of mosquitoes by membrane feeding was similar to infection by direct feeding. Most of the volunteers preferred venipuncture to mosquito bites.

No information about the levels of pro-inflammatory interleukins has been described in children with neurocysticercosis (NCC). The levels of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-5, IL-6, and IL-12 in the cerebrospinal fluid from children with NCC were determined by enzyme-linked immunosorbent assay (ELISA). Twelve children with NCC, six with active and six with inactive disease, and six children without NCC were studied. TNF-alpha was undetectable in CSF from controls and five children with inactive NCC, whereas the levels were significantly higher (median 22.1 pg/ml; P = 0.008) in all children with active NCC. Levels of IL-6 were low in active and inactive NCC patients but two subjects with active subarachnoid disease had high levels. IL-5 and IL-12 were not detected. This study shows that high levels of TNF-alpha are present in CSF from children with active NCC. IL-6 levels are higher when infection occurs in the subarachnoid space.

T lymphocyte activation during dengue is thought to contribute to the pathogenesis of dengue hemorrhagic fever (DHF). We examined the T cell receptor Vbeta gene usage by a reverse transcriptase-polymerase chain reaction assay during infection and after recovery in 13 children with DHF and 13 children with dengue fever (DF). There was no deletion of specific Vbeta gene families. We detected significant expansions in usage of single Vbeta families in six subjects with DHF and three subjects with DF over the course of infection, but these did not show an association with clinical diagnosis, viral serotype, or HLA alleles. Differences in Vbeta gene usage between subjects with DHF and subjects with DF were of borderline significance. These data suggest that the differences in T cell activation in DHF and DF are quantitative rather than qualitative and that T cells are activated by conventional antigen(s) and not a viral superantigen.

A candidate live-attenuated virus vaccine for protection against Venezuelan equine encephalitis (VEE) (designated V3526) was tested in mice to measure the magnitude, duration, and kinetics of virus replication in the blood and the central nervous system and its phenotypic stability after multiple passages in mice and cell culture. All results were compared to parallel experiments with parental virus and the existing VEE virus vaccine, TC-83. Maximum virus titers in the brains of V3526-inoculated mice were between 10- and 100-fold less than those observed in brains of mice inoculated intracranially (i.c.) with either the parental virus or TC-83. Neither V3526 nor TC-83 was lethal in BALB/c mice inoculated i.c.. However, mice inoculated with TC-83 developed acute symptoms lasting at least 14 days. In contrast, i.c. inoculation of TC-83 was uniformly lethal for C3H/HeN mice. V3526 was avirulent in both BALB/c and C3H/HeN mice after i.c. inoculation. The virulence characteristics of V3526 remained unchanged after five serial i.c. passages in mouse brains or after five cell culture passages. Finally, pathologic changes induced after i.c. inoculation of V3526 were consistently less severe and of shorter duration than those observed in TC-83-inoculated mice. Based on these results, V3526 is stable and appears to be significantly less neurovirulent in mice than TC-83.

In this study we documented unexpected moderate-to-severe iodine deficiency in Haitian schoolchildren although they live in a coastal community where presumably they have access to iodine-containing seafood. This fact combined with the lack of an iodized salt supply and endemic lymphatic filariasis makes community distribution of diethylcarbamazine-fortified, iodized salt an attractive strategy for elimination of lymphatic filariasis and iodine deficiency disorders in this area of Haiti. Combining lymphatic filariasis elimination with other public health interventions is one strategy to increase its public health benefit and maximize the impact of limited public health resources.

In malaria holoendemic areas children are anemic, but the exact influence of falciparum malaria on hemoglobin (Hb) concentration remains largely unsettled. Prospective data were therefore collected in children < 24 months of age during five months in a Tanzanian village. Children with mean asymptomatic parasitemia > or = 400/microl had lower median Hb levels during the study than those with mean density < 400/microl. The difference was 9.7 g/L (95% confidence interval [CI] 2.8-17). In children with one or more clinical malaria episodes, the median Hb was 8.3 g/L (95% CI 0.9-16) lower than those without episode. If early treatment failure was recorded, the immediate effect on Hb was particularly important with a mean drop of 17 g/L. Interestingly, at study-end the Hb concentration represented a function of the area under the parasitemia curve (AUPC) during the previous five months, adjusting for age. In conclusion, stepwise deterioration in median Hb levels was found by asymptomatic parasitemia, clinical malaria episode, and most significantly, treatment failure.

From June 1, 1994 to May 31, 1995 a total of 24,700 cases of dengue (7.01/1,000 population) were reported to the laboratory-based surveillance system in Puerto Rico (1991-1994, annual average: 2.55/1,000). Dengue virus 2 predominated. The earliest indicator of epidemic activity was the virus isolation rate in May 1994 (14.0% versus 5.7% average). The male-to-female ratio among cases was 1:1.1; 65.4% were younger than 30 years (the 10 to 19 year age group had the highest incidence, 11.8/1,000). At least 5,687 cases (23.0%) showed a hemorrhagic manifestation; 4,662 (18.9%) were hospitalized, and 40 died (0.2%; 10 laboratory-positive). Two cases documented by laboratory were transmitted by unusual routes--intrapartum and through a bone marrow transplant. Among 2,004 hospitalized cases reported by infection control nurses, 139 (6.9%) fulfilled the criteria for dengue hemorrhagic fever (DHF) and another 13 cases (0.6%) had dengue shock syndrome. This epidemic produced the largest number of hospitalizations, DHF cases, and deaths from any dengue epidemic in Puerto Rico. Severity did not change throughout the year. Surveillance capabilities were maintained by temporary, simplified reporting methods, none of which could be recommended as the single method of choice for surveillance; each must be used (on site, or as a service available from a reference laboratory) at the right time in the epidemic cycle. The utility of comparisons of current and previous data underscores the value of long-term surveillance. Our analysis was unable to document whether significantly increased transmission occurred more often in cities where the water supply was rationed or where the local landfill was closed.

From 1995 to 1997 dengue was reported in Puerto Rico at an average annual rate of 1.75/1,000 population, compared to 6.73 in 1994, an epidemic year. Dengue virus serotypes 1 (DEN-1), -2, and -4 were isolated each year, with DEN-2 predominating in 1995 and 1996, and DEN-4 in 1997. From 1995 through 1997 incidence was highest (0.61-0.77/1,000) in persons under 30 years of age; males and females were equally affected. Among positive cases, 28.3% to 37.9% were hospitalized; 28.9% to 35.2% had hemorrhagic manifestations; at least 1.1% to 1.6% fulfilled the criteria for dengue hemorrhagic fever/dengue shock syndrome; and 0.2% to 0.3% died. Neither hurricane preparations (1995) nor widespread floods (1996) seem to have affected dengue incidence. Most municipalities with the highest laboratory-diagnosed dengue rates in 1995 were in the eastern foothills of the central mountains, an area relatively spared by the 1994 epidemic. In the next two years, at least half of the municipalities with the highest laboratory-diagnosed dengue rates were in the west. The most intense municipal outbreak of this period (DEN-2, Villalba, 1995, rate of 11.67/1,000) is described to highlight the importance of local conditions and epidemiologic history in determining the risk of dengue.

From 1997-1998, we investigated the possible continuous circulation of epizootic Venezuelan equine encephalitis (VEE) virus suggested by a 1983 subtype IC interepizootic mosquito isolate made in Panaquire, Miranda State, Venezuela. The study area was originally covered by lowland tropical rainforest but has been converted into cacao plantations. Sentinel hamsters, small mammal trapping, mosquito collections, and human serosurveys were used to detect active or recent virus circulation. Six strains of subtype ID VEE virus were isolated from hamsters that displayed no apparent disease. Four other arboviruses belonging to group A (Togaviridae: Alphavirus), two Bunyamwera group (Bunyaviridae), and three Gamboa group (Bunyaviridae) arboviruses were also isolated from hamsters, as well as 8 unidentified viruses. Venezuelan equine encephalitis-specific antibodies were detected in 5 small mammal species: Proechimys guairae, Marmosa spp., and Didelphis marsupialis. Mosquito collections comprised of 38 different species, including 8 members of the subgenus Culex (Melanoconion), did not yield any virus isolates. Sera from 195 humans, either workers in the cacao plantation or nearby residents, were all negative for VEE virus antibodies. Sequences of 1,677 nucleotides from the P62 gene of 2 virus isolates indicated that they represent a subtype ID lineage that is distinct from all others characterized previously, and are unrelated to epizootic VEE emergence.

This report describes Trocara virus, a newly recognized member of the genus Alphavirus, that has been isolated from Aedes serratus mosquitoes collected at two widely separated sites in the Amazon Basin. Biological, antigenic and genetic characteristics of the new virus are given. Results of these studies indicate that Trocara virus is the first member of a newly discovered antigenic complex within the family Togaviridae genus Alphavirus. The public health and veterinary importance of Trocara virus is still unknown.

A protocol was created for performing geographically randomized snail surveys for schistosomiasis research using the global positioning system (GPS). This protocol differs from traditional surveys in its ability to accurately map and measure the spatial distribution of snail habitat. The protocol was used to map irrigation ditches, the primary habitat for Oncomelania hupensis, in two residence areas in Sichuan Province, China. From the 7,450 meters of mapped ditches, snail surveys were performed at 203 random sites along the ditch network. Of these, 116 (57.1%) sites had snails. The total number of living snails captured was 2,014, resulting in an average snail density of 0.27 snails per linear meter of potential habitat.